Foto komt in PSE'25 veel donkerder in beeld dan in PSE'21.

Is that in both the Editor and the Organizer?  On the same computer monitor?

Take a look in the Edit>Color Management dialogs that you have in PSE 2025 and PSE 2021.  Are there any different settings between the two?

Here is a screenshot of the two dialogs in Elements 2025.

If that doesn't explain what you are seeing, please attach the original file so that we can examine it.  (If it is a raw file, you may have to zip it in order to upload it to this forum.)